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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/32: Add missing context synchronisation with CONFIG_VMAP_STACK
In-Reply-To: <872477f7c7552d3bb7baf0b302398fcd42c5fcfd.1579885334.git.christophe.leroy@c-s.fr>
References: <872477f7c7552d3bb7baf0b302398fcd42c5fcfd.1579885334.git.christophe.leroy@c-s.fr>
Date:   Sat, 25 Jan 2020 23:15:13 +1100
Message-ID: <87r1znhgvi.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
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Christophe Leroy <christophe.leroy@c-s.fr> writes:
> After reactivation of data translation by modifying MSR[DR], a isync
> is required to ensure the translation is effective.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> Rebased on powerpc/merge-test
>
> @mpe: If not too late:
> - change to head_32.h should be squashed into "powerpc/32: prepare for CONFIG_VMAP_STACK"
> - change to head_32.S should be squashed into "powerpc/32s: Enable CONFIG_VMAP_STACK"
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/kernel/head_32.S | 1 +
>  arch/powerpc/kernel/head_32.h | 2 ++
>  2 files changed, 3 insertions(+)
>
> diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
> index 73a035b40dbf..a6a5fbbf8504 100644
> --- a/arch/powerpc/kernel/head_32.h
> +++ b/arch/powerpc/kernel/head_32.h
> @@ -43,6 +43,7 @@
>  	.ifeq	\for_rtas
>  	li	r11, MSR_KERNEL & ~(MSR_IR | MSR_RI) /* can take DTLB miss */
>  	mtmsr	r11
> +	isync

Actually this one leads to:

  /home/michael/linux/arch/powerpc/kernel/head_8xx.S: Assembler messages:
  /home/michael/linux/arch/powerpc/kernel/head_8xx.S:151: Error: attempt to move .org backwards
  make[3]: *** [/home/michael/linux/scripts/Makefile.build:348: arch/powerpc/kernel/head_8xx.o] Error 1

For mpc885_ads_defconfig.

That's the alignment exception overflowing into the program check
handler:

/* Alignment exception */
	. = 0x600
Alignment:
	EXCEPTION_PROLOG handle_dar_dsisr=1
	save_dar_dsisr_on_stack r4, r5, r11
	li	r6, RPN_PATTERN
	mtspr	SPRN_DAR, r6	/* Tag DAR, to be used in DTLB Error */
	addi	r3,r1,STACK_FRAME_OVERHEAD
	EXC_XFER_STD(0x600, alignment_exception)

/* Program check exception */
	EXCEPTION(0x700, ProgramCheck, program_check_exception, EXC_XFER_STD)


Can't see an obvious/easy way to fix it.

cheers

>  	.endif
>  	subi	r11, r1, INT_FRAME_SIZE		/* use r1 if kernel */
>  #else